Many dry bulk materials are conveniently transported by truck. Typically, these trucks consist of a tractor and an attached trailer for carrying the materials. There are various types of trailers, such as a pneumatic tank trailer. Pneumatic tank trailers are often used to transport dry bulk materials like flour, sugar, plastic pellets, or the like, which can be easily stored in a pneumatic tank trailer's hopper.
The conventional method for unloading the dry bulk material from the hopper is a pneumatic unloading process. This process requires the hopper to have an outlet, usually located at the bottom of the hopper, and an inlet, usually located near the top of the hopper. A blower forces an air stream through a top air pipe and into the inlet of the hopper, thereby pressurizing the hopper interior. The blower also forces the air stream through a material conveying conduit, which has an exit port at its downstream end and is connected to the hopper outlet in the middle of the conduit. As the air stream flows through the conduit, a pressure differential occurs between the hopper and the conduit. This differential propels the dry bulk material located in the hopper to move towards the hopper outlet, into the material conveying conduit, and out the exit port.
Although the above-described method works well with many dry bulk materials, it has a drawback when working with temperature sensitive materials such as plastic pellets, sugar, or the like. Because increased pressure is directly proportional to increased temperature, as the pressure in the hopper and the material conveying conduit increases, so does the temperature. The temperature in the hopper and the material conveying conduit often rises above the melting point of the plastic pellets, thereby causing the plastic pellets to melt. Many problems are associated with melting temperature sensitive materials such as plastic pellets. For example, the composition of the pellets breaks down, rendering them useless. Also, the melting plastic can stick to the hopper, the hopper outlet, or the material conveying conduit, requiting lengthy and expensive clean up procedures.
As a result thereof, there are various methods attempting to resolve this problem. One method is to have water-enclosed sheath cool the pipe conveying the air stream to the hopper. This method, however, is not successful because water is not always available at the unloading site and discharge of the water is inconvenient and not environmentally acceptable. Another method is placing cooling fins on the material conveying conduit. This method is also unsuccessful because the fins are expensive, bulky and heavy, and are only marginally effective.
Finally, the most common method is to restrict the blowers to run at a reduced pressure, thereby keeping the temperature below the plastic pellet's melting point. Although this prevents the pellets from melting, it introduces a different set of difficulties. First of all, the pressure must be monitored to insure that it does not get too high, thereby melting the pellets. Secondly, the process now takes a longer time because the lower pressure does not move the pellets as quickly. Thirdly, the pressure differential between the hopper and the material receiving conduit is not as drastic, and therefore the pellets are more likely to get clogged in the hopper outlet.
Therefore, what is needed is a method and system to remove the dry bulk material from the hopper using a pneumatic unloading process, whereby the air temperature is kept below the dry bulk material's melting point and the air pressure is kept significantly high. Furthermore, the method and system should be self-contained on the trailer and not be overly expensive, bulky, or heavy.